Blooms of the cyanobacteria Limnoraphis cf. birgei in a volcanic Lake of El Salvador, Central America

Abstract

In May 2018, the proliferation of a filamentous cyanobacteria was detected for the first time in Lake Coatepeque, a deep, oligotrophic, volcanic lake in western El Salvador, Central America. Since that year, four events of proliferation of this cyanobacteria have been recorded, which had an impact on the inhabitants' activities that depend on the lake's water. Sampling campaigns were conducted both during bloom and non-bloom conditions between in May 2018 and March 2021 in Lake Coatepeque. In these campaigns, surface samples were collected using a sampling bottle at five sites in the lake and physico-chemical data was also registered. Material was characterized by optical microscopy; cell abundance was quantified using a Sedgwick-Rafter camera on an inverted microscope and with the aid of an ocular reticle. In the five blooms events, the causative organism was observed forming uniseriate filaments of 21-24 µm and trichomes 18-22 µm wide, with aerotopes irregularly distributed along the trichome and with a firm yellowish hyaline sheath. According to the morphological characteristics, the species corresponds to the description of Limnoraphis birgei, however, molecular and biochemical data is needed to confirm the species identity. Proliferations of L. cf. birgei generated brown surface agglomerations, which in some cases reached cell concentrations exceeding 900,000 cells mL-1. No human or animal intoxications were reported. This is the first report of occurrence and proliferation of Limnoraphis in El Salvador and one of the few cases reported worldwide.

Full text

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CYANOBACTERIAL BLOOMS
Blooms of the cyanobacteria Limnoraphis cf.
birgei in a volcanic Lake of El Salvador, Central
America
Rebeca Quintanilla*, Oscar Amaya, Jeniffer Guerra
Laboratorio de Toxinas Marinas, Universidad de El Salvador, Final Av. Héroes y Mártires del
30 de julio, zip code 1101 San Salvador, El Salvador.
* corresponding author’s email: cesiah.quintanilla@ues.edu.sv
Abstract
In May 2018, the proliferation of a lamentous cyanobacteria was detected for the rst time in
Lake Coatepeque, a deep, oligotrophic, volcanic lake in western El Salvador, Central America.
Since that year, four events of proliferation of this cyanobacteria have been recorded, which had
an impact on the inhabitants’ activities that depend on the lake’s water. Sampling campaigns
were conducted both during bloom and non-bloom conditions between in May 2018 and March
2021 in Lake Coatepeque. In these campaigns, surface samples were collected using a sampling
bottle at ve sites in the lake and physico-chemical data was also registered. Material was
characterized by optical microscopy; cell abundance was quantied using a Sedgwick-Rafter
camera on an inverted microscope and with the aid of an ocular reticle. In the ve blooms
events, the causative organism was observed forming uniseriate laments of 21-24 µm and
trichomes 18-22 µm wide, with aerotopes irregularly distributed along the trichome and with
a rm yellowish hyaline sheath. According to the morphological characteristics, the species
corresponds to the description of Limnoraphis birgei, however, molecular and biochemical data
is needed to conrm the species identity. Proliferations of L. cf. birgei generated brown surface
agglomerations, which in some cases reached cell concentrations exceeding 900,000 cells mL-
1. No human or animal intoxications were reported. This is the rst report of occurrence and
proliferation of Limnoraphis in El Salvador and one of the few cases reported worldwide.
Keywords: cyanobacteria bloom, crater lake, oligotrophic
https://doi.org/10.5281/zenodo.7034997

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CYANOBACTERIAL BLOOMS
Introduction
The increase in the occurrence of algal blooms
is considered as one of the main effects of
eutrophication and climate change over aquatic
systems (O’Neil et al., 2012; Paerl and Otten,
2013)estuarine, and marine ecosystems.
Recent research suggests that eutrophication
and climate change are two processes that
may promote the proliferation and expansion
of cyanobacterial harmful algal blooms.
In this review, we specically examine the
relationships between eutrophication, climate
change and representative cyanobacterial
genera from freshwater (Microcystis,
Anabaena, Cylindrospermopsis. In recent
years, there has been an increase in the report
of harmful algal blooms in freshwater bodies
of El Salvador, particularly in the central-
western part of the country (Quintanilla et
al., 2020). In May 2018, the proliferation of
a lamentous cyanobacteria was detected for
the rst time in Lake Coatepeque (Fig. 1), a
deep, oligotrophic, volcanic lake in western
El Salvador, Central America.
Until March 2021, ve events of proliferation of
this cyanobacteria have been recorded, which
had an impact on the inhabitants’ activities
that depend on the lake’s water. The study
presented here describes the cyanobacterial
bloom events in Lake Coatepeque, as well as
the taxonomic identication of the causative
species by means of light microscopy.
Fig. 1. Mats of cyanobacterial blooms detected in Lake
Coatepeque. El Salvador.
Material and Methods
Site description
Lake Coatepeque is a crater lake located in
the southwest of El Salvador (13°51’ N,
89°32’ W), at the altitude of 740 m above sea
level (Fig. 2). It has an area of 24.8 km2 and
is an endorheic water body, thus its drainage
is through subsurface inltration. Maximum
depth in the lake is 115 m and the walls that
surround it are between 200 m and 300 m.
Surface water temperature ranges from 22°C
to 31°C along the year. The climate in this
area is characterized by a dry season that
takes place between November and March,
and a warm rainy season between April and
October. By 2021, the lake has been classied
as oligotrophic, with total phosphorus values
ranging from 0.18 mg L-1 to 0.88 mg L-1
(MARN, 2021).
The lake is an important local resource, since
it is used for artisanal shing, recreation,
irrigation and, water supply to the surrounding
population. It also has a large national
signicance as a touristic destination, mainly
because it regularly changes its color from
blue to bright turquoise, which was previously
thought to be caused by cyanobacteria
(Espinoza et al., 2013).
Sampling and laboratory analysis
Sampling campaigns were conducted both
during bloom and non-bloom conditions
between May 2018 and March 2021 in Lake
Coatepeque. In these campaigns, surface
water samples were collected using a sampling
bottle in at least ve sampling points during
each sampling in the lake. Data on water
temperature, pH and total dissolved solids
(TDS) was recorded in situ on each sampling
point, using a thermometer, pH meter, and an
electrical conductivity meter, respectively.

114
CYANOBACTERIAL BLOOMS
Fig. 2. A) Location of Lake Coatepeque in El Salvador,
and B) Panoramic photo of Lake Coatepeque.
Phytoplankton samples were characterized by
optical microscopy. During bloom events, cell
abundance was quantied using a Sedgwick-
Rafter chamber on an inverted microscope
and with the aid of an ocular reticle. During
non-bloom conditions, cell abundance was
quantied using Utermöhl chambers; cell
abundance was calculated as number of cells
per milliliter. Length and width of laments
and trichomes were measured using an
imaging software.
Results and Discussion
Bloom events took place both during dry
season (January, February, and November),
as well as during rainy season (May). None of
the blooms spread to the entire lake, but rather
occurred within specic locations near to the
shores. During bloom events, temperature
ranged from 22.5 °C to 28.6 °C, pH from 8.3
to 9.3, and TDS from 943 ppm to 1259 ppm.
In the four blooms events, the causative
organism was observed forming uniseriate
laments of 21-24 µm wide and trichomes
18-22 µm wide (n = 30), and with a rm
yellowish hyaline sheath that surpass
trichomes. Cells are shorter than wide and
have aerotopes irregularly distributed along
the trichome. Trichomes are cylindrical, not
constricted at cell walls and with rounded end
cells (Fig. 3).
Fig. 3. Filaments of Limnoraphis cf. birgei. Scale bar
represents 20 µm.
Initially, the causative species of the blooms
was identied as belonging to the genera
Lyngbya (Quintanilla et al., 2020). However,
further literature revision and re-examination
of samples has allowed to re-identify the
causative organism in the genera Limnoraphis.
Komárek et al. (2013)tentatively identied
as Lyngbya robusta, recently increased in
abundance in Lake Atitlán, Guatemala, and
since 2008 annual water-blooms occurred.
This was one from the rst known cases
of L. robusta water-blooms worldwide. A
polyphasic evaluation of L. robusta using 16S
rRNA gene sequencing, cytomorphological
markers, and ecological characteristics
was made. This species had several unique
features. It produced aerotopes that were
irregularly spaced in cells; cyanotoxins were
not found, and it xed nitrogen in spite of the

115
CYANOBACTERIAL BLOOMS
lack of heterocytes. It contained a high amount
of carotenoids, which caused an unusual
brown color of the macroscopic scum on the
water level. Molecular phylogenetic analyses
using the 16S rRNA gene showed that L.
robusta, together with few other planktic
species, formed a clade, separated from
typical Lyngbya species. The main diacritical
markers of this clade were the planktic type
of life and formation of gas vesicles in cells.
Based upon molecular, morphological and
ecological data, a new genus Limnoraphis
was proposed with four species. © Czech
Phycological Society (2013 proposed the
separation of planktonic Lyngbya species
into the new genera Limnoraphis based on a
polyphasic classication approach. Currently,
there are four species identied within this
genera: Limnoraphis birgei (G. M. Smith)
J. Komárek, E. Zapomelová, J. Smarda, J.
Kopecký, E. Rejmánková, J. Woodhouse, B.
A. Neilan & J. Komárková 2013, Limnoraphis
criptovaginata (Schkorbatov) J. Komárek,
E. Zapomelová, J. Smarda, J. Kopecký, E.
Rejmámková, J. Woodhouse, B. A. Neilan & J.
Komárková 2013, Limnoraphis hieronmuysii
(Lemmermann) J. Komárek, E. Zapomelová,
J. Smarda, J. Kopecký, E. Rejmánková, J.
Woodhouse, B. A. Neilan & J. Komárková
2013, and Limnoraphis robusta (Paracutty)
J. Komárek, E. Zapomelová, J. Smarda, J.
Kopecký, E. Rejmánková, J. Woodhouse, B.
A. Neilan & J. Komárková 2013 (Komárek
et al., 2013)tentatively identied as Lyngbya
robusta, recently increased in abundance
in Lake Atitlán, Guatemala, and since 2008
annual water-blooms occurred. This was
one from the rst known cases of L. robusta
water-blooms worldwide. A polyphasic
evaluation of L. robusta using 16S rRNA
gene sequencing, cytomorphological markers,
and ecological characteristics was made.
This species had several unique features.
It produced aerotopes that were irregularly
spaced in cells; cyanotoxins were not found,
and it xed nitrogen in spite of the lack of
heterocytes. It contained a high amount of
carotenoids, which caused an unusual brown
color of the macroscopic scum on the water
level. Molecular phylogenetic analyses
using the 16S rRNA gene showed that L.
robusta, together with few other planktic
species, formed a clade, separated from
typical Lyngbya species. The main diacritical
markers of this clade were the planktic type
of life and formation of gas vesicles in cells.
Based upon molecular, morphological and
ecological data, a new genus Limnoraphis
was proposed with four species. © Czech
Phycological Society (2013.
According to the morphological distinction
of Limnoraphis species made by Komárek et
al. (2013) tentatively identied as Lyngbya
robusta, recently increased in abundance
in Lake Atitlán, Guatemala, and since 2008
annual water-blooms occurred. This was
one from the rst known cases of L. robusta
water-blooms worldwide. A polyphasic
evaluation of L. robusta using 16S rRNA
gene sequencing, cytomorphological markers,
and ecological characteristics was made.
This species had several unique features.
It produced aerotopes that were irregularly
spaced in cells; cyanotoxins were not found,
and it xed nitrogen in spite of the lack of
heterocytes. It contained a high amount of
carotenoids, which caused an unusual brown
color of the macroscopic scum on the water
level. Molecular phylogenetic analyses
using the 16S rRNA gene showed that L.
robusta, together with few other planktic
species, formed a clade, separated from
typical Lyngbya species. The main diacritical

116
CYANOBACTERIAL BLOOMS
markers of this clade were the planktic type
of life and formation of gas vesicles in cells.
Based upon molecular, morphological and
ecological data, a new genus Limnoraphis
was proposed with four species. © Czech
Phycological Society (2013, the species found
in Lake Coatepeque matches better to the
description of Limnoraphis birgei; however
some feature resemble those of Limnoraphis
robusta. Filaments´ width matches that of L.
birgei exclusively; however, trichomes width
matches with both L. birgei and L. robusta.
It has been identied that Limnoraphis
trichomes width might decrease during
blooms, resembling the morphology of other
Limnoraphis species (Salazar-Alcaraz et al.,
2021), and thus making species identication
difcult by means of morphological features
alone. As expected, this highlights the need
of incorporating molecular and biochemical
data in order to conrm the identity of the
species found in Lake Coatepeque.
Proliferations of L. cf. birgei generated
brown surface agglomerations (Fig. 1), which
in some cases reached cell concentrations
exceeding 900,000 cells mL-1. Bloom events
were considered as such when there was a
noticeable change in water color due to an
increase in cyanobacteria cell abundance.
During non-bloom conditions, maximum
cell abundance was 62,559 cells mL-1; while
during bloom conditions cell abundance
ranged between 168,360 and 929,280 cells
mL-1 (Fig. 4).
Filaments were also found in samples from 10
m and 20 m depth but in lower abundances. In
some blooms, Limnoraphis co-occurred with
Microcystis aeruginosa. Limnoraphis blooms
have been scarcely reported in freshwater
ecosystems. The reported events have taken
Fig. 4. Cell abundance of L. cf. birgei in Lake
Coatepeque from May 2018 to December 2020 period.
place at Santa María del Oro crater lake in
México (Salazar-Alcaraz et al., 2021), Lake
Ontario in Canada (Zastepa and Chemali,
2021), Habanilla reservoir in Cuba (Comas-
González et al., 2017), Lake Titicaca in Peru
(Komárková et al., 2016), Clear Lake in
United Stated (Kurobe et al., 2013)and Lake
Atitlán in Guatemala (Rejmánková et al.,
2011).
Blooms of Limnoraphis have been related
to the upwelling of nutrient rich water
(Rejmánková et al., 2011). Particularly,
Limnoraphis robusta has been reported to
occur in oligotrophic to mesotrophic water
bodies when phosphorus concentrations
increase (Komárek et al., 2013; Salazar-
Alcaraz et al., 2021). Additionally, some
strains have the ability to x nitrogen through
diazocytes (Rejmánková et al., 2011).
Probably this is the case of the Limnoraphis
strain present in Lake Coatepeque, since it has
been conrmed that the lake is oligotrophic.
Further research on the species is needed,
both to better understand the potential harm
its blooms might represent for the local

117
CYANOBACTERIAL BLOOMS
inhabitants, as well as to contribute to the
morphological and molecular studies of the
Limnoraphis clade.
During blooms events, no human or animal
intoxications were reported; however, toxins
production needs to be monitored since local
population consume the lake’s water without
any previous treatment, and some species of
this genera have been reported to produce
trace amounts of cylindrospermopsin and
saxitoxins (Rejmánková et al., 2011)
Acknowledgements. We thank Fundación
Coatepeque for its support in nancing and
providing logistical facilities for sampling
campaigns, and the project IAEA-RLA7025
for its support in consolidating LABTOX-
UES technical capacities and nancing
participation in ICHA.
References
Comas-González, A., Labaut-Betancourt, Y.,
Peraza-Escarrá, R. (2017). An. Biol. 39, 1-6.
Espinoza, J., Amaya, O., Rivera, W., Ruíz,
G., Escobar, J. (2013). Bioma 4, 43-46.
Komárek, J., Zapomělová, E., Šmarda, J.,
Kopecký, J., et al., (2013). Fottea 13, 39-52.
Komárková, J., Montoya, H., Komárek, J.
(2016). Hydrobiologia 764, 249-258.
Kurobe, T., Baxa, D. V., Mioni, C.E., Kudela,
R.M., et al., (2013). Springerplus 2, 1-12.
MARN, 2021. Evaluación de la calidad del
agua del Lago de Coatepeque. San Salvador.
32 p.
O’Neil, J.M., Davis, T.W., Burford, M.A.,
Gobler, C.J. (2012). Harmful Algae 14, 313-
334.
Paerl, H.W. and Otten, T.G. (2013). Science
342, 433-434.
Quintanilla, R., Amaya, O., Guerra, J. (2020).
Rev. Cuba. Investig. Pesq. 37, 92-97.
Rejmánková, E., Komárek, J., Dix, M.,
Komárková, J., Girón, N. (2011). Limnologica
41, 296-302.
Salazar-Alcaráz, I., Ochoa-Zamora, G.G.,
Hernández-Almeida, O.U., Palomino-
Hermosillo, Y.A., et al., (2021). Rev. Mex.
Biodivers. 92, e923485.
Zastepa, A. and Chemali, C. (2021). Data in
Brief 35, 106800.